On Thu, Apr 20, 2017 at 01:40:13PM +1000, Michael Ellerman wrote:
> "Paul E. McKenney" <paulmck@xxxxxxxxxxxxxxxxxx> writes:
>
> > diff --git a/include/linux/srcutree.h b/include/linux/srcutree.h
> > index f2b3bd6c6bc2..0400e211aa44 100644
> > --- a/include/linux/srcutree.h
> > +++ b/include/linux/srcutree.h
> > @@ -24,25 +24,75 @@
> ...
> > +/*
> > + * Per-SRCU-domain structure, similar in function to rcu_state.
> > + */
> > struct srcu_struct {
> > - unsigned long completed;
> > - unsigned long srcu_gp_seq;
> > - atomic_t srcu_exp_cnt;
> > - struct srcu_array __percpu *per_cpu_ref;
> > - spinlock_t queue_lock; /* protect ->srcu_cblist */
> > - struct rcu_segcblist srcu_cblist;
> > + struct srcu_node node[NUM_RCU_NODES]; /* Combining tree. */
> > + struct srcu_node *level[RCU_NUM_LVLS + 1];
> > + /* First node at each level. */
> > + struct mutex srcu_cb_mutex; /* Serialize CB preparation. */
> > + spinlock_t gp_lock; /* protect ->srcu_cblist */
> > + struct mutex srcu_gp_mutex; /* Serialize GP work. */
> > + unsigned int srcu_idx; /* Current rdr array element. */
> > + unsigned long srcu_gp_seq; /* Grace-period seq #. */
> > + unsigned long srcu_gp_seq_needed; /* Latest gp_seq needed. */
> > + atomic_t srcu_exp_cnt; /* # ongoing expedited GPs. */
> > + struct srcu_data __percpu *sda; /* Per-CPU srcu_data array. */
> > + unsigned long srcu_barrier_seq; /* srcu_barrier seq #. */
> > + struct mutex srcu_barrier_mutex; /* Serialize barrier ops. */
> > + struct completion srcu_barrier_completion;
> > + /* Awaken barrier rq at end. */
> > + atomic_t srcu_barrier_cpu_cnt; /* # CPUs not yet posting a */
> > + /* callback for the barrier */
> > + /* operation. */
>
> This change seems to have had the non-obvious effect of breaking the
> powerpc KVM build.
>
> Because struct kvm contains two srcu_structs which are located
> before the kvm_arch struct, the increase in size of srcu_struct has
> caused the offset from the start of struct kvm to kvm_arch to be too big
> for some of our asm.
>
> struct kvm {
> spinlock_t mmu_lock;
> struct mutex slots_lock;
> struct mm_struct *mm; /* userspace tied to this vm */
> struct kvm_memslots *memslots[KVM_ADDRESS_SPACE_NUM];
> struct srcu_struct srcu;
> struct srcu_struct irq_srcu;
> ...
> struct kvm_arch arch;
>
>
> Example error:
> arch/powerpc/kvm/book3s_hv_rmhandlers.S:617: Error: operand out of range (0x000000000000b328 is not between 0xffffffffffff8000 and 0x0000000000007fff)
>
> Where line 617 is:
> lwz r7,KVM_LPID(r9)
>
> And the KVM_LPID constant comes from asm-offsets.s. The diff of old vs
> new is:
>
> -->KVM_LPID 17752 offsetof(struct kvm, arch.lpid) #
> +->KVM_LPID 45864 offsetof(struct kvm, arch.lpid) #
>
>
> We can probably just fix it by changing the asm to keep the address of
> kvm_arch in a register, and then offset from that.
Ouch!
What do you need from me?
Thanx, Paul
